The court on Thursday overturned a 20-year-old ruling that said corporations can be prohibited from using money from their general treasuries to pay for campaign ads. The decision almost certainly will also allow labor unions to participate more freely in campaigns and threatens similar limits imposed by 24 states.

The justices also struck down part of the landmark McCain-Feingold campaign finance bill that barred union- and corporate-paid issue ads in the closing days of election campaigns.

Opponents of campaign finance reform and fans of the First Amendment are rejoicing. Others are frightened of the influx of free speech from corporations and unions in a mid-term election year.

The AP notes that the ruling may affect similar limits set in 24 states, and Tom Goldstein of SCOTUSBlog observes: "The decision presumably applies equally to state and local elections, given that the Court recognizes a 1st Amendment right."

The case stemmed from a movie critical of then-pres. candidate Hillary Clinton, which the FEC said violated the Bipartisan Campaign Reform Act, also known as McCain-Feingold. The FEC argued the movie violated section 203 of BCRA, which prohibits corporations and unions from using non-PAC money in ads that mention a candidate for office, and sections 201 and 311, which set up disclosure requirements.

Reform advocates were disheartened when the Court refused to rule on the case last term, when it was originally argued. Instead, justices asked for a rehearing in order to consider whether the Court should overrule two previously settled cases as well. Those cases, McConnell v. FEC and Austin v. Michigan Chamber of Commerce, were victories for reformers -- victories that were snatched away today.

On Wednesday, the Court overturned Austin, as well as a part of McConnell that placed restrictions on independent expenditures by corporations.

** Disclosure requirement: Any corporation that spends more than $10,000 in a year to produce or air the kind of election season ad covered by federal restrictions must file a report with the Federal Election Commission revealing the names and addresses of anyone who contributed $1,000 or more to the ad’s preparation or distribution.

** Disclaimer requirement: If a political ad is not authorized by a candidate or a political committee, the broadcast of the ad must say who is responsible for its content, plus the name and address of the group behind the ad.

Update: From the opinion:

"The First Amendment does not permit laws that force speakers to retain a campaign finance attorney, conduct demographic marketing research, or seek declaratory rulings before discussing the most salient political issues of our day...

The Government may not render a ban on political speech constitutional by carving out a limited exemption through an amorphous regulatory interpretation."

Continued:

While some means of communication may be less effective than others at influencing the public in different contexts, any effort by the Judiciary to decide which means of communications are to be preferred for the particular type of message and speaker would raise questions as to the courts’ own lawful authority. Substantial questions would arise if courts were to begin saying what means of speech should be preferred or disfavored. And in all events, those differentiations might soon prove to be irrelevant or outdated by technologies that are in rapid flux...

Courts, too, are bound by the First Amendment. We must decline to draw, and then redraw, constitutional lines based on the particular media or technology used to disseminate political speech from a particular speaker. It must be noted, moreover, that this undertaking would require substantial litigation over an extended time, all to interpret a law that beyond doubt discloses serious First Amendment flaws. The interpretive process itself would create an inevitable, pervasive, and serious risk of chilling protected speech pending the drawing of fine distinctions that, in the end, would themselves be questionable. First Amendment standards, however, “must give the benefit of any doubt to protecting rather than stifling speech.”